Generation of electric currents



. Juhe 2-, 1931. L. J. s"|v| AN GENERATION OF ELECTRIC CURRENTS Filed April 29, 1926 FiqJ. I 57.2.

Effccfiye A. C. lnduciance a 0 Superimposed Dirccf Currenr lnvenfo/ I Lean J. S/v/an by 47f Patented June 2, 1931 UNITED STATES PATENT OFFICE LEON J. SIVIAN, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK GENERATION 015 ELECTRIC CUR'REN'IS Application filed April 29,

This invention relates to generation of electric currents.

An object of the invention is to provide for simply and efficiently generating band frequency currents. This object may be realized by the provision of band frequency generators having frequency distributions of output energy sufficiently similar to the frequency distribution of energy of speech waves to be capable of serving satisfactorily in testing telephone circuits and instruments, as, for example, for operating telephone receivers employed as sound sources for testing telephone transmitters by the general method disclosed in Arnold et al. Patent 1,426,807, August 22, 1922, entitled Method of and system for testing transmitters or receivers.

A feature of the invention relates to employing an electric space discharge amplifying device in generating currents of a large number of frequencies and so associating a source of alternating electromotive force with the device that the cyclical variations of the electromotive force contribute materially to the production of the multiplicity of the frequencies of the currents generated.

In the preferred form of the invention the electric space discharge amplifying device is an oscillation generator, (for instance of the general type well known as the Colpitts oscillator), which has the value of its tuning inductance, or inductance upon which the frequency of oscillations depends, continuously varying cyclically, (a feature claimed in the Isles Patent 1,606,792, November 16, 1926), the variation being accomplished in accordance with the present invention by the variation of the magnetic permeability of ferromagnetic material in the magnetic circuit of the inductance. Specifically, the permeability is varied by superimposing the magnetic flux created in the magnetic circuit of the tuning inductance by the oscillation current, upon a magnetic flux created by a low frequency alternating current, for example, a current having a frequency of the order of 16 cycles per second, this superimposed low frequency flux being of such a magnitude as to carry the magnitude of the tuninginductance up and down cyclically through the 1926. Serial No. 105,400.

desired range of values between its minimum value, at which the oscillator frequency will have the maximum value desired, and its maximum value, at which the oscillator frequency will have the minimum value desired.

Other objects and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings in which Figs. 1, 3, 4 and 5 represent four different band frequency generators each embodying a form of the invention; and Fig. 2 is a curve for facilitating explanation of the invention.

In Fig. 1 is shown a vacuum tube oscillator of the well known Colpitts type, including an electric space discharge tube 6 and an oscillation circuit comprising condensers 7 and 8 and an inductance coil 9. The coil 9 has a ferromagnetic core. Thus the inductance of the coil, and consequently the frequency of the oscillator, can be varied by superimposing the oscillation current flowing through the coil upon a current flowing through the coil and varying at a rate low in comparison to the oscillation frequency, since the effective A. C. inductance of a coil on a ferromagnetic core varies with the magnitude of the direct or low frequency current upon which it is superimposed, in the general manner indicated by the curve in Fig. 2, which is plotted between the effective alternating current inductance of the coil as ordinates and direct exciting current as abscissze, the A. C. voltage across the coil being of constant value and frequency and the direct current ranging from the value Zero to a value corresponding to a point in the region of the top of the knee of the BI'I curve, or in other words in the region where the magnetic material of the core becomes saturated by the direct flux. A generator 10 having a frequency of, say 16 cycles per second, sends current through a circuit comprising a coil 11 of high impedance for the oscillation frequency, the primary winding 12 of a low frequency transformer 18, and coil 9. This current causes the inductance of coil 9 to be varied at the rate of 32 complete cycles per second. Preferably, where it is desired that the of the tube.

oscillations generatedsimulate voice currents, the limiting values between which the in ductance is thus Varied are such that the oscillation frequency varies between the limits of400 and 2000 cycles per second. Preferably, the value ofthe. current supplied from generator 10' to coil: 91 is such that thefluxln the core of the coil varies over the upwardly concave portion of its BH curve during at least a considerable portion of each cycleof this low frequency current. The chokecoil 11 prevents the flow of. oscillation frequency currents into the generator 10. Since, in practice, the 16 cycle voltage is quite large compared with the voltage produced by the oscillator,-.it is; advisable; to provide means to prevent, the 1'6- cyclev voltage from. being efiectivelyimpressedion the grid and the plate of the tube. Such meansfis afforded by the transformer 13 and the variable condenser 14 and variable resistance 15 inthe secondary circuit: of the transformer. Voltage from across resistance 15 is impressed on the grid of the tube, and by proper adyustment of. condenser 14:- and resistance 15v this voltage is} given the proper amplitude and phase to compensate for, or neutralize the effects of, the voltages otherwise impressed from the sourceilObn the grid: andthe plate If desired, the generator 10 may be separated from tube 61- by blocking condenser for currentsLo-f-the frequency pro-- duced by'generator 10.

lathe operation of the system. of Fig. 1 the frequency of the oscillations generated varies cyclically and continuously in accord-.

ance. with the variations which current from source 10 produces in the value of'the inductance of coil 9. Thus the oscillator generates only one fundamental frequency at a time, that frequency varying between wide limits and the rate of variation preferably being gradual and preferably being small compared, to the lower l miting oscillation frequency where it is desired to insure that theoscillationswil-l contain few components andon-ly those whose frequenciesare known, as will be further explained later. It has been found that the simulation. of voice currents. is closer when 7 the inductance isv varied at a frequency of approximately 32 cycles per second, or even somewhat more slowly, than when the variation is at a: considerably higher frequency in the audible frequency range.

here it is desired. that the oscillation frequency vary at a. uniform rate, the preferable range. of variation of the effective A. G. inductance is. a range corresponding roughly to the portion of. the curve of Fig. 2 lying between, the origin and the value of; magnetizing current indicated by a. This insures operation over a part of this curve for which the alternating current inductance,

and therefore the oscillation frequency,

varies rapidly with the magnetizing current,

necessary inductive over therange of frequencies which the oscillator generates. This circuit 9, 22 is tuned to the frequency of generator 10, and therefore tends to prevent voltage of the fre quency produced by generator from being applied to the grid and the plateof tube 6..

This resonating circuit 9, 22, therefore supplements the. action of the compensating circuit 13, 1e, in preventing voltage of the frequency produced by generator 10 from being applied to the grid. and the plate of tube 6., In Fig. 3 two resistances 15 are employed, instead of a single resistance 15 as in ig. 1,. in order to obtain greater flexibility in adjusting the phase and the amplitude of the compensating potential independently of each other. Condenser 23 in Fig. 3 supplements the action of coil 11 in preventing current of the oscillation frequency from reaching generator 10. In the system of Fig. 3 the oscillation frequency; isvaried in a manner similar to that set forth above in describing induc'tanceof coil 9, as a result of the variable Fig. l.

In the systenisof Fig. 3 and Fig. l,

by the space current batteries shown; for, if desired, the source 10, or any othersuitable low frequency alternating current source, having a frequency either the same as or different from that of source 10,. may be employedas the space currentsource.

In Fig. 4 is shown a Colpitts oscillator circuit in which the oscillation circuit comprises condensers 7 and 8 and an inductance 3 0, the inductance being variable to produce the-1e quired cyclical variation of the oscillation frequency. The inductance comprises a winding Slhaving a magnetic core 32, and also compr'ses, as part of the magnetic circuit of the winding, a magnetic annulus or ring'33 mounted on a non-magnetic member 34 rotated by apower driven shaft 35 preferably at such aspeed that the value of the inductance changes at the rate of the order of 10 complete cycles per second, the variation of the inductance being due to the fact that the thicknessof ring 83, in the directhe operation of the system of Fig. 1, by variation of the it is not I that the space current be supplied.

- 39 connected to generator 10.

tions of its radii, varies gradually from a minimum value at one point on the ring to a maximum value at the diametrically opposite point, so that the revolution of the ring changes the reluctance of the magnetic cirrespectively. If the space current source for the tube were a D. C. source, the output of the oscillator would be such that it could be regarded approximately, at least, as of the character of the output of the system shown in Fig. 1, the frequency varying over the range from 400 to 2000 cycles per second at a rate of ten cycles per second. It should be noted that, since the rate of variation of the inductance is slow compared with the frequencies of oscillation, the cycle of 1/10 second may conveniently be considered as subdivided into smaller periods during which the energy would be largely confined to small fractions of the entire spectrum width. During a certain small fraction of a cycle, the energy output may, in such a consideration, be roughly regarded as concentrated in the region between 1150 and 1250 cycles, during an immediately succeeding equal small fraction of the cycle, between 1250 and 1350 cycles, etc. That is, although a continuous frequency change implies a continuous change of shape or distortion of each cycle of the generated wave or, in other words, a modulation with its attendant undesired modulation products, the gradualness of the frequency change in the present instance substantially nullifies such undesirable effects. This feature is important wherever the oscillator output current is to be used in measurements involving elements possessing pronounced frequency and non-linear distortion characteristics (as for instance in testing a commercial telephone instruments and the human ear) since it insures the production of awave, which while simulating to a considerable extent a voice wave, has a simple and known frequency characteristic. An alternating current source 10, preferably having a frequency of the order of 60 cycles per second, supplies filament heating current and plate current for tube 6 through the secondary windings 36 and 37 respectively of a transformer 38, having a primary winding The use of this alternating current source renders the frequency spectrum and the frequency distribution of the output energy of the oscillator more complex than as just described for the case of the oscillator with a direct current plate source, and tends to increase the number of frequencies in the wave generated by the oscillator, on account of the rectification of the space current. The frequency distribution of the output energy of the oscillator of Fig. 4 is made still more complex by the fact t iat oscillations are maintained only during less than one-half of the total time the system is in operation.

A stopping condenser is employed to prevent alternating current from source 10' from flowing in the frequency determining or oscillation circuit, where it might cause an unstable operation that would be undesirable. A compensating circuit, similar to the compensating circuit of Fig. 1, comprises a secondary winding 13 of transformer 38, and condenser 14 and resistance 15. In this circuit the winding 13 corresponds to the secondary winding of transformer 13 in Fig. 1, and as in Fig. 1, the condenser 14 and resistance 15 serve to adjust the phase and amplitude of the compensating voltage delivered to the grid-filament circuit by the secondary winding of the transformer. The voltage across resistance 15 is applied to the grid of tube 6, as in Fig. 1, and balances or neutralizes any grid voltage due to cycle current passing from the plate circuit of the tube through the stopping condenser 40 into the oscillation circuit. The condenser 41, across winding 37, tends to by-pass around that winding any current of oscillation frequency which the plate circuit retard coil fails to choke back from the plate circuit. The shaft 35 may be driven from generator 10', or from any other suitable power source, either directly or with any desired speed ratio.

The use of the alternating current generator 10 eliminates any necessity for a direct current source for the plate circuit of tube 6 and enables the use of a single A. C. generator as a source of energy for the circuit as a whole, supplying energy for the plate circuit, the filament circuit, and the compensating circuit, and driving shaft 35. Further, as indicated above, the asymmetric conductivity of tube 6 for the 60 cycle current from source 10 results in production of harmonics and consequent increase in the number of frequencies in the wave generated by the oscillator.

In the operation of the system of Fig. 4 the oscillation frequency is gradually varied by variation of the value of inductance 30, due to the rotation of ring 33, and as indicated above, the number of oscillation frequencies so produced is augmented by the rectifying action of tube 6 upon the A. C. space current supply for the tube.

A band frequency oscillation generator in which the oscillation frequency is varied by a motor-driven variable inductance connected in the oscillation circuit, is claimed in Isles Patent 1,606,792, November 16, 1926.

The method of generating an alternating current of variable frequency which consists in cyclically varying the resonance of an oscillation circuit is covered in Arnold et al. Patent 1,573,367, February 16, 1926.

Fig. 5 shows a band frequency generator comprising two electric space discharge tubes 51 and 52 connected in tandem. Their filaments, connected in series, are energized from a secondary winding 53 of a transformer 55%,

5 and their plate currents aresupplied from a secondary winding 55 of the transformer. The prin'iarywinding 56 of the transformer is energized from an alternating current source preferably having a frequency of the or- 10 'der of 60 cycles per second. A resistance-57 in accordance with the plate current.

In the operation of the system, on account of the rectifying action of both the grid-fila- ,ment and plate-filament circuits the output currents of tubes 51 and 52 contain a large number of harmonics of the sixty cycle current, or of the frequency of generator 10. The output current of tube 51 passes through condenser 59 and theprimary winding 60 of an interstage transformer 61. The secondary winding 62 of transformer 61 impresses the harmonics generated in the output circuit of tube 51 upon the grid of tube 52, through a condenser 63 and grid leak resistance 64, with the addition of still other frequencies due to the non-linearity of the B+H curve of the material of the magnetic circuit of the transformer. Tube 52 further multiplies these frequencies, so that tube 52 sends currents of many frequencies through its output circuit including condenser 66 and the primary winding 67 of an out-put transformer 68, and these currents in turn generate currents of many frequencies in the secondary winding 69 of the transformer, which supplies the work circuit (not shown). The condenser 63 and resistance 6t'provide an average negative grid potential for tube 52 in addition to that impressed from resistance 57. The combination of condenser and grid leak has a time constant which is low compared with that of an ordinary oscillator or amplifier where a similar combination is used toprovide anegative grid potential. It is preferably, but not necessarily 1/60 of a second or the same as that of the potential impressed on the plates.

There results a periodic charge of. the condenser when the grid goes positive and a similar periodic discharge through the gridleak resistance. This produces a sudden stoppage of the space current witha resultant further 6? production of harmonics Thus it is clear that even though the first stage of the'amplifier, including tube 51, were omitted from the circuit of Fig. 5, the second stage, including tube 52, would serve as a band frequency generator. The ultimate efiect of the Whole rent as a function of the grid and plate potentials; and (3) the non-linearity of the mag f netic characteristics of the ferromagnetic material in the Coils and transformers employed.

Condensers 59 and 66 and the choke coils in the space current circuits of the tubes separate the pulsating current delivered by the winding 55 from the high frequency currents,

in the two branches of the plate circuit of each tube. The capacities of the condensers may, if desired, be made small enough to prevent the passage, through transformers 61 and 68, of not only the pulsations from winding 55 but also their first few harmonics, so that only currents of frequencies higher than, say, a few hundred cycles per second, pass through the windings and 67 Theinvention is not limited to the values specifically mentioned above with regard to frequency ranges, the frequencies of the alternating current sources involved, and the like, as considerable latitude may be exercised in selecting such values. For example, where it is desired to employ a system of the type shown in Fig. 1 or Fig. 3 in frequency modulation of an oscillator wave of a frequency of the order of the frequencies commonly desig nated as in the carrier frequency range, the

source 10 may be a telephone transmitter circuit or like source of voice currents, varying the inductance of coil 9 through a range of values corresponding to oscillation frequencies of the order just mentioned. What is claimed is: 1. In a band frequency oscillation generator, an oscillation circuit for determining the" frequency of the current produced by said generator, said circuit including an inductance having a fixed magnetic circuit C0111? prising solid magnetic material, and means for continuously varying the permeability of said material so as to cause the frequency of said generator current to correspondingly continuously vary.

2. An oscillation current generator comprising an electric space discharge device, an

oscillation circuit for determining the fre quency ofsaid generator, said circuit including an inductance having magnetic material.

in its magnetic circuit, and means for superimposing the magnetic flux created in the magnetic circuit of said inductance by the oscillation current upon a magnetic flux so varying as to cause the frequency of said recurrently.

ator and the value of 3. The method of controlling the frequency of an alternating current generator including an inductance which has a fixed magnetic circuit including solid magnetic material and is traversed by current enerated by the generwhich inductance determines the frequency of the generator at any given time, which comprises so varying the permeability of said material continuously and cyclically as to cause continuous and cyclical variation of the frequency of the current as generated within the audible range.

4. In combination, an electric space discharge tube having an oscillation circuit, comprising inductance, for causingsaid tube to "generate oscillations, the frequency of said oscillations at any given time being dependent upon the value of said inductance and said inductance having ferromagnetic material in its magnetic circuit, a sourceof alternating current, and means for so associating said source and said inductance that current from said source creates in said material a continuously and cyclically varying magnetic flux, said source having such electromotive force that said flux variations result in variations in the permeability of said material which cause the oscillations generated by said tube to continuously and cyclically vary in frequency over a frequenc range including frequencies substantially higher than the frequency of said source.

5. An oscillation generator comprising an electric space discharge device, an oscillation circuit therefor, means comprising a source of alternating electromotive force cooperating with said device and said circuit, in such manner that the variations in the voltage of said source cause said oscillator to generate currents of a multiplicity of desired frequencies, means connecting said source with said device so that the source tends to impress potentials on said device, and means, including circuit connections between said source and said device, for preventing the operation of said oscillation generator from being affected by said potentials.

6. An alternating current generator, an inductance included in said generator, said inductance having a magnetic circuit including magnetic material and being traversed by current generated by the generator, and the value of said inductance determining the frequency of the generator at any given time, means for so varying the permeability of said material continuously and cyclically as to cause continuous and cyclical variation of the frequency of the current as generated within the audible frequency range, a source of alternating electromotive force included in said means, said source tending to impress undesired voltage variations on said discharge device, and means cooperating with said induc- 'tance to form a shunting path of low impedance for current of the frequency of said voltage variations, in shunt relation to said dis charge device with respect to said source.

7. In an oscillation generator comprising an electric space discharge device having an anode, a cathode, and an impedance control element, an oscillation circuit for determining the frequency of said generator, said circuit including an inductance having ferromagnetic material in its magnetic circuit, and means for superimposing the magnetic flux created in the magnetic circuit of said inductance by the oscillation current upon a magnetic flux so varying as to cause the frequency of said generator current to vary uniformly and recurrently, said means comprising a source of alternating electromotive force for supplying alternating current to said inductance, said source tending to impress potential variations of the frequency of said source upon the control electrode and upon the anode of said discharge device, and means for so associating said source with said control electrode as to counteract the effect of said potentials upon the currents generated by said oscillation generator, said last means com rising a circuit for impressing potentials rom said source upon said control electrode, and said circuit comprising means whereby the amplitude and the phase of said compensating potentials may be adjusted.

8. In combination, an electric space discharge device having an anode, a cathode, and an impedance control element for controlling the impedance of the space discharge path between said anode and said cathode, and means cooperating with said device for causing said device to produce output current representing such frequency distribution of energy as to simulate speech current sufiiciently closely to be capable of serving satisfactorily for actuating a telephone receiver to produce sound waves for testing telephone transmitters, said means comprising an alternating current source separate from said device generating an electromotive force of a frequency of the order of a frequency at least as low as 100 cycles per second, and said means further comprising means, including circuit connections so associating said device and said source as to cause the cyclical variations of said electromotive force to contribute to the production of the multiplicity of the frequencies of said currents.

9. In combination, an electric space discharge device having an anode, a cathode, and an impedance control element for controlling the impedance of the space discharge path between said anode and said cathode, and means cooperating with said device for pro ducing currents of such magnitude, frequency and relative time of occurrence as to simulate speech currents sufiiciently closely to be capable of serving satisfactorily for actuating a telephone receiver to produce sound waves for testing telephone transmitters, said means comprising an alternating current source separate from said device and continuously and independently of said tube generating an electromotive force of a constant frequency substantially lower than the maximum frequency.

of said current and of the order of a frequency at least as low as 100 cycles per second, and said means further comprising means, includ- "ing circuit connections so associatingsaid of the frequencies of said currents and so that "a portion of said electromotive force is applied between said impedance control element and said. cathode in such manner that said electromotive force has no resultant eifect on the operation of said device per se.

10. Incombination, an electric space discharge amplifying device, and means comprising coupled output and input circuits for said device for causing said device to generate oscillations, said circuits comprising a tuned circuit including an inductance having inits magnetic circuit ferromagnetic material, and a means causing said material to operate on a non-linear portion of its B -H curve during at least a portion of the time said device is generating oscillations.

11. The method of varying over a desired frequency band, the frequency of oscillation of an electric space discharge oscillator including a tuning inductance having ferromagnetic material in its magnetic circuit, which comprises subjecting said magnetic circuit to a magnetomotive force --of such 4 value as to cause the magnetic flux density of the upwardly concave the first oscillator.

in said material to correspond to the region part of its B-H curve during at least a portion of the time said oscillator is generating oscillations.

v 12; Frequency modulating means comprising an oscillationcircuit and means for supplying energy thereto, said circuit including inductance for determining the oscillation frequencies of oscillation currents in said circuit, said inductance having magnetic material in itsmagnetic circuit, and said first means also comprising means for creating, in said magnetic circuit a magnetic flux upon which the flux therein due to said oscillation currents is superimposed, the instantaneous magnitude of which first flux determines the frequency of said oscillation currents.

13. In combination, an oscillator, a second oscillator comprising a resonant frequency determining circuit, an inductance with-magnetic material in its magnetic circuit, and means controlled by the first oscillatorto vary the reactance of said inductancein accordance with the instantaneous amplitude of the oscillations of said circuit containing having magnetic material in its magnetic,

circuit, and means controlled by another oscillator to vary the frequency of the first oscillator in accordance with the instantaneous amplitude of the oscillations of said other oscillator. V

15 A method of generating varying oscillations which comprises generating continu-. ous oscillations of dlfferent frequencies ln a plurality of systems, the frequency in one 7, system being determined by'a current-com, trolled reactance, and varying said react-ance' in accordance with the, instantaneous amplitude of a current produced by another system.

16. Frequency modulating, meanscomprising an oscillation circuit and means for supplyingenergy thereto, said circuit including inductance for determining the oscillation frequency of said circuit, said inductance having magnetic material in its magnetic circuit, andvsaid first means also comprising means controlled by an electric generator to vary the reactance of said inductance and so to produce oscillations varying in frequency in accordance with the instantaneous amplitude of the current generated;

In witness whereof, I hereunto subscribe my name this 27th day of April, A. D. 1926. LEON J. SIVIANL Lao 

